Re: [PATCH v2] media: qcom: camss: fix VFE pm domain off

[Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>]

On 11/29/24 13:06, Bryan O'Donoghue wrote:
> On 29/11/2024 08:48, Vladimir Zapolskiy wrote:
>> On 11/28/24 21:39, Barnabás Czémán wrote:
>>> Fix NULL pointer check before device_link_del
>>> is called.
>>>
>>> Unable to handle kernel NULL pointer dereference at virtual address
>>> 000000000000032c
>>> Call trace:
>>>    device_link_put_kref+0xc/0xb8
>>>    device_link_del+0x30/0x48
>>>    vfe_pm_domain_off+0x24/0x38 [qcom_camss]
>>>    vfe_put+0x9c/0xd0 [qcom_camss]
>>>    vfe_set_power+0x48/0x58 [qcom_camss]
>>>    pipeline_pm_power_one+0x154/0x158 [videodev]
>>>    pipeline_pm_power+0x74/0xfc [videodev]
>>>    v4l2_pipeline_pm_use+0x54/0x90 [videodev]
>>>    v4l2_pipeline_pm_put+0x14/0x34 [videodev]
>>>    video_release+0x2c/0x44 [qcom_camss]
>>>    v4l2_release+0xe4/0xec [videodev]
>>>
>>> Fixes: eb73facec2c2 ("media: qcom: camss: Use common VFE pm_domain_on/
>>> pm_domain_off where applicable")
>>> Tested-by: Yassine Oudjana <y.oudjana@protonmail.com>
>>> Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
>>> Signed-off-by: Barnabás Czémán <barnabas.czeman@mainlining.org>
>>> ---
>>> Changes in v2:
>>> - Add backtrace to the commit message.
>>> - Link to v1: https://lore.kernel.org/r/20241122-vfe_pm_domain_off-
>>> v1-1-81d18f56563d@mainlining.org
>>> ---
>>>    drivers/media/platform/qcom/camss/camss-vfe.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/media/platform/qcom/camss/camss-vfe.c b/drivers/
>>> media/platform/qcom/camss/camss-vfe.c
>>> index
>>> 80a62ba11295042802cbaec617fb87c492ea6a55..1bf1473331f63b9ab106d21ea263c84d851c8a31 100644
>>> --- a/drivers/media/platform/qcom/camss/camss-vfe.c
>>> +++ b/drivers/media/platform/qcom/camss/camss-vfe.c
>>> @@ -595,7 +595,7 @@ void vfe_isr_reset_ack(struct vfe_device *vfe)
>>>     */
>>>    void vfe_pm_domain_off(struct vfe_device *vfe)
>>>    {
>>> -    if (!vfe->genpd)
>>> +    if (!vfe->genpd_link)
>>>            return;
>>>        device_link_del(vfe->genpd_link);
>>>
>>
>> I object to this change, there might be a problem in the code, however it
>> is not yet identified.
>>
>> vfe->genpd is not NULL, if vfe_pm_domain_on()/vfe_pm_domain_off() are
>> called appropriately, the "fix" does not fix the real problem, it veils it.
>>
>> -- 
>> Best wishes,
>> Vladimir
>>
>>
> 
> Let's walk through the logic.
> 
> vfe->genpd =
> 
> Can happen in vfe_subdev_init();
> 
> vfe_pm_domain_on() can fail @ vfe->genpd_link =
> 
> If it fails then I _suppose_ we are still calling vfe_pm_domain_off() at
> least that's the only logically way I see this error can manifest.

There should be no room for suppositions, the source code is open.

If the described by you case is true, and vfe_pm_domain_on() fails,
then vfe_pm_domain_off() shall not be called, otherwise that's the
real problem and it shall be fixed instead of being veiled by the
proposed change.

> @Barnabás can you confirm that this is the case ?
> 
> If not, can you please provide more detail ?

The change does not describe how to reproduce the problem, which commit
base is tested, which platform is testes, there is no enough information,
unfortunately.

--
Best wishes,
Vladimir